MacBooks come with power adapters that provide a certain wattage (for example 87 W) required to keep the computer running and charge the battery. If used with a lower-wattage power adapter (for example 61 W), there might not be enough power to keep the computer running. However, could such a lower-wattage power adapter be used to fully recharge the battery if the computer is kept turned off?
Could even a low-wattage iPhone charger be used for this, although it would probably take a long time?
Update: The question concerns newer MacBooks with USB-C chargers.
Best Answer
Assuming you are referencing the MacBooks and MacBook Pros with USB-C ports (2016 and up), the short answer is yes, a low power adapter could charge the MacBook which requires a higher power adapter to function.
(and yes, it will take a very, very long time)
As for Macs with the MagSafe adapter, since the DC-In board (or MagSafe power board) "checks" the power coming it, if it's not of the right voltage/wattage, it won't charge.